1. Field of the Invention
The invention relates to a measurement arrangement typically for road thickness measurement.
2. Discussion of the Background
Civil engineering materials are often non-homogenous comprising a matrix of two or more products with different particle size and physical properties.
FIG. 1 shows part of a typical road structure with a wearing surface layer and a sub base layer of courser material.
Typical of these materials are concrete asphalt and bituminous macadam. When these materials are used as surfacing or cladding for structures such as roads and buildings, it is sometimes necessary to measure the thickness of the surfacing to establish the engineering strength of the structure.
The usual method of measuring the thickness of these materials is to take samples of the material using a coring tool. This can give a very accurate measure if properly used but it suffers from a number of disadvantages. The integrity of the original surface is destroyed by taking a core sample and even if properly repaired it may lead to early deterioration of the surface. Coring of small area structures such as road reinstatements is impractical as the area of the core may be a substantial fraction of the area of the reinstatement. A core sample provides only a spot measurement which may not be representative of the general condition of the rest of the structure.
Non intrusive measurement techniques have proved difficult due to the non-homogenous matrix of materials employed in such structures.
According to the invention there is provided a device for measuring the thickness of a non-homogenous medium and comprising means for transmitting pulses of electromagnetic energy through the material; first means for receiving a first reflected energy signal; second means spaced from the first means for receiving a second reflected energy signal; and, means for calculating material thickness using information derived from both the first and second reflected signals.
According to a further aspect of the invention there is provided a pulse radar method applicable to the calculation of the thickness of a non-homogenous meduim, comprising passing into the medium from a first location at the outer surface, a pulse of electromagnetic energy and receiving at second and third locations at the surface a reflected pulse and calculating the material thickness using information derived from both received and reflected pulses.